Various types of multi-bit drivers are presently available in the market that provide a plurality of readily available tool bits in a single easy-to-use multi-bit driver which minimizes the time for bringing a tool bit into and out of operation and also decreases the time for selecting one tool bit from another.
One such multi-bit driver is disclosed in U.S. Pat. No. 3,750,729 issued Aug. 7, 1973 to Lemieux and entitled Multiple Driver Tool. This multi-bit driver has a chamber for holding a plurality of drivers (also commonly known as tool-bits) for screws and the like. For each driver, a guided slide is retained in a co-operating guide track channel for movement between a retracted position and an extended in-use position, and is connected to the driver by an elongate connector. In the extended in-use position, the driver extends through a passage at the forward end of the chamber and projects forwardly therefrom.
An annular wall that defines the chamber tapers inwardly to the inner end of the passage. When any one of the drivers is moved forwardly along the chamber towards its extended position, its outer end is guided into the inner end of the passage by the tapered annular wall. This is the specific means that is provided for guiding each of the drivers into the passage, as specifically stated at column 2, starting at line 57, and is the only guiding means taught. There is no other means taught that guides the selected tool bit into the passage when the tool bit is moved to its extended position.
In order for the driver to be guided into the passageway, the connector that connects the slide to the driver must be sufficiently flexible to permit the driver to follow along the tapered annular wall of the housing to the passage. The flexible connector is in the shape of a tube and is formed from strip of material tightly wound in the shape of a helix, with no space between adjacent coils. The material is either metal or suitable plastic, thus providing a comparatively rigid but bendable connector, as specifically stated at column 2, lines 45 and 46. A helically coiled compression spring (see column 3, line 38), with spaces between adjacent coils, surrounds each connector in its retracted position, to bias the connector and the attached driver to the retracted position, yet still allow the connector to be equally flexible in all directions, as it is moved to its extended position.
It can be seen that the connector with the spring around it has an effective cross-section that is radially consistent. In other words, the effective shape and diameter of the connector is the same in any radial direction away from the axial center. Accordingly, the connector bends consistently in any angular direction. No provision has been made for causing or allowing the connector to bend more in one angular direction than in another angular direction, or to resist bending in more in one angular direction than in another angular direction.
Depending on the orientation of the entire device, this angular deflection in any direction may cause the driver to try to enter the passage from a skewed direction when the driver is moved towards its extended position, which is highly undesirable, since the driver might tend to jam against the annular wall. This potential problem is heightened by the fact that the working end of the driver may have a shape (such as a wide slot screwdriver bit, or other Philips or Robertson screwdriver bits) that readily catches on the entrance to the passageway at the termination of the tapered annular wall, or catches on the annular wall, as the driver is being moved to its extended position. Further, the overall shape of the connector changes on an ongoing basis due to the fact that the adjacent coils of the connector contact each other. When the connector flexes and returns to its rest position, the adjacent coils bind slightly, thus precluding the connector from returning to the exact same shape each time. The changed shape causes the driver to be skewed, and thus not be aligned with the passage.
Another problem with the multi-bit driver disclosed in the Lemieux patent is that in order to preclude rotation of the driver with respect to the housing, it uses round tool bits having two radial keys disposed on the back end of each tool bit. Each key engages a co-operating slot formed in the housing and extending radially outwardly from the passage. With such an arrangement, the two keys must fit closely into the respective slots, or else the driver will be loose during use, which is unacceptable. Accordingly, the slots must be only marginally wider than the respective key, thus making insertion of the key into the slot an operation requiring precise alignment. Although the drivers are constrained such that each of the keys generally aligns with the respective slot when the drivers are in their retracted positions, the keys may readily be displaced out of proper alignment by uncontrolled deflection during movement to the extended position. This is caused, at least in part, by the overall flexibility of the connector that connects the driver to the slide.
This particular problem is even greater in multi bit drivers that employ hexagonally shanked drivers. Such hexagonally shanked tool bits must register and align almost perfectly with the co-operating hexagonal bit receiving channel in the bit chuck, otherwise the selected tool bit will not slide through the bit chuck into its extended position. Only very minimal deflection or twisting of these tool bits as they are urged from their retracted position to their extended position can be tolerated, as the edges of the hexagonal flutes will catch on the inner wall of the bit chuck, adjacent the back end of the hexagonal bit receiving channel. Since the tool bit shank is hexagonal, the bit extension must have qualities that minimize twisting to ensure proper tool bit insertion into the channel. The bit extension needs to be flexible in the radial direction and rigid in the transverse direction, ensuring the driver is inserted into the channel the same way each and every time, thereby greatly reducing the chance of jamming.
Another disadvantage of the constant cross-section connectors as disclosed in the Lemieux patent, is that since they are equally flexible in all radial directions, there is the definite possibility of lateral flexing of any extended drivers. Accordingly, a driver that is partially extended could readily tangle with the other drivers.
U.S. Pat. No. 5,325,745 issued Jul. 5, 1994, to Koehler, discloses a Screwdriver, wherein extensions from the bits (referred to as drivers in the Lemieux patent and commonly referred to as tool bits) are not of a constant cross-section, in order to provide increased flexibility in a direction aligned radially with its central longitudinal axis. The screwdriver as taught has a plurality of bit assemblies retained within the hollow interior of a housing. Each bit assembly has a bit with a rearwardly disposed hexagonal end. A leaf spring is attached to the central portion of the bit and extends laterally outwardly to terminate in a thumb piece disposed externally to the housing. In use, the thumb piece is manually slid forwardly until it abuts against the leading end of its slot. It is then pushed radially inwardly, in a transverse direction to the original movement, so as to move the hexagonal end of the bit immediately in front of a cooperating hexagonal recess. In order to accomplish this radially inwardly directed movement, the leaf spring must be quite flexible in that direction, and not stiff. Accordingly, it could not be used in the multi-bit driver as specifically taught by Lemieux, which requires a stiff yet still bendable connector. It can be seen from the usage description that engaging a bit requires numerous cumbersome steps. In addition the back of the bit must be perfectly aligned with the hexagonal recess before fitting the bit shank into the recess is possible.
There is a need for a multi-bit driver that is easily used, allows for very quick selection of tool bits, that prevents the loss of tool bits through misuse, that provides for a rugged dependable design, that prevents jamming on extension or retraction of the selected tool bit, and minimizes the chance of the tool bits interfering one with another by means of controlling the lateral stiffness of the tool bit extensions.